Black and white view after splitting window
If I'm understanding your question correctly, the issue is that you are in Solid view and want to see the Material Preview.

Click this button at the top right of the 3D viewport and you will see the material attached to the object.

 

As an aside, you can change the color of objects in Solid shading mode by scrolling down towards the bottom of the Material Properties tab and choosing a color for the object under Viewport Display.